Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$126.27	10.636%	$139.7001	$139.70	$139.70	$139.70
Purchase #2	$56.73	8.530%	$61.5691	$61.57	$61.55	$61.60
Purchase #3	$11.71	3.302%	$12.0967	$12.10	$12.10	$12.10
Purchase #4	$36.28	12.699%	$40.8872	$40.89	$40.90	$40.90
Purchase #5	$67.95	13.546%	$77.1545	$77.15	$77.15	$77.20
Purchase #6	$247.89	10.304%	$273.4326	$273.43	$273.45	$273.40
Purchase #7	$114.70	3.703%	$118.9473	$118.95	$118.95	$118.90
7 purchase totals =	$661.53		$723.7875	$723.79	$723.80	$723.80